My dentist asked me to go from invisalign tray 9 to 12. Is this safe?

Doing things out of sequence can have undesirable results. If you are in pain, it may mean that the teeth are moving too quickly. One of the touted advantages of Invisalign is that they are fairly painless and are designed to minimize discomfort. Also, that given cost is based on the number of trays and length of treatment, I would also recommend against jumping trays. They should always be replaced, in order, every 10-14 days, depending on your needs. However, without all the information, I can't really give any other advice. Like the other two doctors, I would highly recommend speaking to your dentist about this and clearly express your reservations. Your teeth are too valuable to take unnecessary risks with.

Hi, first of all invisalign does not cause much pain while moving teeth. And if they are moving too quickly, you got to be careful and change aligners in no less than 2 weeks. I would be very cautious to jump the sequence and discuss again the reason for jump suggestion with the dentist.

Definitely invisalign doesn't recommend this.  The most I have ever heard of is cutting down the time form 14 to 10 days.  However, no one can second guess clinical information we don't have.  He may well hav good reasons.